The aim of the project is to characterize the interactions of the formyl peptide ligands with formyl peptide receptors and to use these peptides as models for developing the rapid mix flow cytometer. A family of formyl peptides with fluorescein isothiocyanate conjugated at positions 2 through 7 has been generated and their binding to receptors has been characterized by flow cytometry with respect to binding and cell physiology (Freer). These studies have suggested that the family of peptides may be used in the future to detect sites of contact by photoaffinity crosslinking. Ye and Prossnitz are producing mutant receptors whose kinetics are being characterized in the rapid mix flow cytometer. The molecular assemblies, receptor processing, and desensitization of these receptors are being evaluated. Kinetic methods have been used to determine the interactions of the receptors with signal transducing G proteins. (Domalewski, J. Receptor Research, in press, 1996)